NEW YORK (Reuters Health) - Allergic reactions to soy may be a cause of asthma symptoms in some workers at soy processing plants, a new study suggests.

Soy is among the most common sources of food allergies, and some studies have found that people who work in soy processing have higher-than-average rates of respiratory symptoms such as wheezing.

Those findings raised the question of whether breathing in soy "dust" may lead to airway inflammation and asthma in some workers.

For the new study, researchers at the U.S. Centers for Disease Control and Prevention (CDC) assessed employees at a Tennessee soy processing plant, at the request of workers who believed that their respiratory symptoms were related to workplace exposures.

They found that the 281 workers they interviewed had higher-than-average rates of wheezing and current, doctor-diagnosed asthma. Nine percent had asthma -- 70 percent higher than the rate among U.S. adults, based on a national health survey from the early 1990s. In addition, 29 percent had suffered bouts of wheezing in the past year, double the prevalence among U.S. adults.

Blood tests further showed that the workers were more likely to have immune system antibodies against soy, when compared against 50 healthcare workers used for a "control" group.

Twenty-one percent had IgE antibodies against soy, versus 4 percent of the control group; IgE antibodies are involved in triggering allergic reactions. Employees with IgE antibodies against soy were three times more likely than their co-workers to have asthma or asthma-like symptoms.

The findings are the first to show an association between soy allergy and asthma symptoms among soy workers, according to lead researcher Dr. Kristin J. Cummings, of the CDC's National Institute for Occupational Safety and Health.

They suggest that such allergies are responsible for at least some workers' asthma, she said in an interview.

The plant her team studied was responsible for taking crushed soy "flakes" and further processing them into soy powder products. Cummings said she and her colleagues believe that airborne soy dust was responsible for some workers' allergy development and respiratory symptoms.

She also suggested that soy workers who think they have respiratory problems related to their job discuss it with their doctors.

Cummings noted that not all workers with asthma and asthma-like symptoms had antibodies to soy. But that, she said, does not mean that their problems are unrelated to their jobs. Other workplace exposures -- to mold, for example, or high levels of dust in general -- may contribute to asthma in some people.